Adverse effects of oral anticoagulants (warfarin, fluindione mainly) are bleeding complications and concern 13% of hospitalizations, approximately 17,000 admissions per year. They constitute 12.3% of iatrogenic adverse effect according to the latest results of the survey conducted by the haute autorité de santé (HAS). A study realized in 2000, with 2976 patients, shows that 28.8% of patients were outside of any therapeutic range (<2 or> 4.5). In 2003, a third of french biologists had no knowledge of the indication of VKA treatment of patients at the INR measurement, and more than fifty percent in 2000. When the therapeutic range was known, the value of the INR remained outside it in 30% of cases. The median time between INR equilibration phase was 5 to 6 days, while the recommended time is 2 to 4 days. A quarter of patients in phase equilibrium treatment did not have a measure of INR at least once a month. Followed over a period of a year, patients spent 40% of the time with a value of INR outside the therapeutic range, high-risk area of recurrent thrombosis or hemorrhage. That is why they require regular monitoring of INR.